As an example of a vehicle brake device configured to control a braking force applied to a vehicle depending on the amount of brake operation by a driver, for example, vehicle brake devices disclosed in JP-A-2010-167915 (Patent Document 1) and JP-A-9-328069 (Patent Document 2) have been known. In the vehicle brake devices, an input piston and a pressing piston are held in a separated state with a predetermined interval (a stroke), and thus a braking force based on a control oil pressure generated by an accumulator and a linear valve is applied to a wheel cylinder depending on the movement of the input piston. In vehicle brake devices, a master system constituted by a master cylinder or the like forming a pressing piston plays an important role.
According to the vehicle brake device described in Patent Document 1, when responsiveness is delayed in the braking pressure due to the linear valve, the valve is turned ON, and responsiveness is improved by also using a driving fluid pressure adjustment device pressure. Furthermore, according to the vehicle brake device described in Patent Document 2, in regard to two types of means for performing a brake assist, a breakdown of one is detected, and when the vacuum booster fails, the brake pressure is increased according to the brake operation.
However, the device disclosed in Patent Document 1 is for the purpose of securing responsiveness of the brake pressing, but does not detect and assist a failure of the master system related to the master cylinder. Furthermore, in the device described in Patent Document 2, even though a failure of a vacuum booster can be detected, a failure of the master system cannot be detected.